The present invention relates to a photoresist composition suitable for lithography utilizing high-energy radiation such as a far ultraviolet ray including eximer laser, electron beam, X-ray, radiation or the like.
Recently, with development of higher integration of an integrated circuit, formation of a submicron pattern is required. Eximer laser lithography has attracted special interest for such a requirement, particularly for it enables production of 64 MDRAM and 256MDRAM. As aresist suitable for such eximer laser lithography process, a so-called chemical amplification type resist has been adopted which utilizes an acid catalyst and chemical amplification effect. In the chemical amplification type resist, solubility of portion irradiated with a radiation in an alkaline developer is changed through a reaction utilizing an acid catalyst generated from an acid generator in the irradiated portion, and by this, a positive or negative pattern is obtained.
In the chemical amplification type positive resist, an acid generated in the irradiated portion diffuses by post heat treatment (post exposure bake: hereinafter, abbreviated as PEB), and acts as a catalyst for changing solubility of irradiated portion in a developer. Such a chemical amplification type positive resist generally comprises a resin component which is alkali-insoluble or alkali slightly soluble by itself, but is converted to alkali-soluble by the action of an acid, and an acid generator which generates an acid by the action of an radiation.
Excimer lasers have a defect that they generate a standing wave formed by interference of t he reflected light and the incident light in a film when they are irradiated on a resist film placed on a substrate having a high reflectivity, because they have a high coherence. For example, when the intensity of the light in a resist film becomes uneven by such a standing wave, a phenomenon occurs in which a side of resist pattern becomes wave-shaped, so-called the standing wave effect. When a side of resist pattern becomes wave-shaped due to the standing wave effect, it is difficult to keep a fixed width of pattern line. In order to suppress the standing wave effect, it is general to suppress the interference in the film by adding a light-absorbing ingredient in the resist. When, however, such a light-absorbing ingredient is used, a problem arises that the light energy in the bottom of the resist film becomes weak and the profile of pattern becomes a tapered shape of a bottom-expanded form. This phenomenon lowers the resolution. In addition, due to the light interference described above, when the light exposure is carried out through a so-called half-tone mask having a small transmittance even at a ask ed part, sometimes a phenomenon (called side lobe) occurs that a perforation that is not present in the mask is formed in an unexposed part. Formation of such a side lobe causes a serious problem in the production of semiconductor integrated circuits.
In addition, generally in the lithography, it is demanded to form a pattern of high fidelity to the original mask pattern even if the focus is somewhat moved during the radiation irradiation. In other words, a photoresist having a deeper depth of focus or a wide focus margin is demanded.
The purpose of the present invention is to provide a positive working photoresist composition which is excellent in various resist properties including sensitivity, resolution, film-forming property, coating property, heat resistance and so on; excellent also in pattern profile and depth of focus; hard to cause standing wave effect in particular, and capable of forming an almost perpendicular and smooth pattern side face even on a substrate having a high reflection. As the result of extensive studies for attaining such purpose, the present inventors have found that a positive working photoresist composition having excellent properties can be obtained by adding a specific compound in the resist together with a resin and an acid-generator. The present invention has been completed based on such fact.